docs: def _prepare_coords(lons1, lats1, lons2, lats2):
      """
      Convert two pairs of spherical coordinates in decimal degrees
      to numpy arrays of radians. Makes sure that respective coordinates
      in pairs have the same shape.
      """
      lons1 = numpy.radians(lons1)
      lats1 = numpy.radians(lats1)
      assert lons1.shape == lats1.shape
      lons2 = numpy.radians(lons2)
      lats2 = numpy.radians(lats2)
      assert lons2.shape == lats2.shape
      return lons1, lats1, lons2, lats2